This invention relates to an oriented multilayer structure of polypropylene (referred to as PP) and a co-polyester laminated together with an adhesive and a method for making such structure.
The general foods packaging industry is forever looking for the perfect film that has excellent sealability to itself or to other films, has excellent bonding capabilities to such materials as films, vacuum deposited metals, inks, and adhesives, has excellent optical properties yielding high gloss, low haze, and high clarity, and has improved barrier properties yielding low gas transmission to gases such as air, nitrogen, carbon dioxide and hydrocarbons. Many attempts have been made to produce such a film based on single layer or multiple layer structures. Many conventional, single and multiple layer structures have been used with a moderate degree of success, such as saran-coated polypropylene, glassine, and the like. A critical characteristic that needs the greatest attention is the barrier properties. This characteristic is important because in supermarket type stores, where there are many types of products from foods to hardware, it is easy to contaminate a food product such as potato chips with a pungent odor from a soap or solvent that may be placed next to it.
Prior to the present invention, numerous multilayer films were developed for use in the packaging industry to create a film having the above mentioned desired properties. U.S. Pat. No. 4,501,797 discloses a multilayer film for use in the packaging industry comprising five layers of a polypropylene layer, an adhesive layer of anhydride modified polypropylene, a barrier layer of ethylene vinyl alcohol copolymer or nylon, a heat sealable layer, and a sealant layer. It is disclosed that this film is economically competitive to make and has a combination of attributes including, as functional physical properties, high barrier to gaseous transmission through the film, and as perceived properties, high gloss, transparency, and stiffness.
U.S. Pat. No. 4,501,798 discloses a film material having seven layers wherein the first three layers are a nylon, the fourth layer is an adhesive layer, the fifth layer is a polyethylene or a blend of ethylene polymers, the sixth layer is an adhesive layer and the seventh layer is a sealant layer. This patent also discloses that in another embodient the first three layers are a single layer of nylon. It is disclosed that this film is adapted for use in conventional packaging equipment to economically package a variety of products.
U.S. Pat. No. 4,352,849 discloses a co-extruded, heat-shrinkable, multilayer polyolefin packaging film having a core layer of ethylene vinyl acetate copolymer blended with ethylene propylene copolymer sandwiched between thin layers of copolymer of propylene. It is disclosed that this multilayer of polyolefin film has shrink tensions approximating those of polyvinyl chloride (PVC) films, has good optical qualities, has a wide shrink temperature range, has sealability, has resistance to tear propagation properties, and has none of the undesirable qualities of PVC film such as noxious odors and corrosive by-products.
European Patent Office publications (EP220619-A, EP220620-A, and EP220621-A) disclose biaxially drawn, co-extruded polypropylene film laminates of 3-5 layers containing a co-polyester layer of terephthalic acid, isophthalic acid, ethylene glycol, or butane diol where the carboxylic acids can contain additional functional groups to improve bonding between the layers. The laminates can also contain heat or cold sealable layers and a silicone layer.
None of the prior art discloses the present invention.